Direct Experimental Determination of the Reaction Kinetics of the Simplest Criegee Intermediate, CH2OO, and Isoprene

(Statement of Responsibility) by Zachary C. J. Decker(Thesis) Thesis (B.A.) -- New College of Florida, 2016RESTRICTED TO NCF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE(Bibliography) Includes bibliographical references.This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.Faculty Sponsor: Shipman, Steve

Nighttime chemical transformation in biomass burning plumes : A box model analysis initialized with aircraft observations

Biomass burning (BB) is a large source of reactive compounds in the atmosphere. While the daytime photochemistry of BB emissions has been studied in some detail, there has been little focus on nighttime reactions despite the potential for substantial oxidative and heterogeneous chemistry. Here, we present the first analysis of nighttime aircraft intercepts of agricultural BB plumes using observations from the NOAA WP-3D aircraft during the 2013 Southeast Nexus (SENEX) campaign. We use these observations in conjunction with detailed chemical box modeling to investigate the formation and fate of oxidants (NO3, N2O5, O3, and OH) and BB volatile organic compounds (BBVOCs), using emissions representative of agricultural burns (rice straw) and western wildfires (ponderosa pine). Field observations suggest NO3 production was approximately 1 ppbv hr–1, while NO3 and N2O5 were at or below 3 pptv, indicating rapid NO3/N2O5 reactivity. Model analysis shows that >99% of NO3/N2O5 loss is due to BBVOC + NO3 reactions rather than aerosol uptake of N2O5. Nighttime BBVOC oxidation for rice straw and ponderosa pine fires is dominated by NO3 (72, 53%, respectively) but O3 oxidation is significant (25, 43%), leading to roughly 55% overnight depletion of the most reactive BBVOCs and NO2

Nighttime and daytime dark oxidation chemistry in wildfire plumes: an observation and model analysis of FIREX-AQ aircraft data

Wildfires are increasing in size across the western US, leading to increases in human smoke exposure and associated negative health impacts. The impact of biomass burning (BB) smoke, including wildfires, on regional air quality depends on emissions, transport, and chemistry, including oxidation of emitted BB volatile organic compounds (BBVOCs) by the hydroxyl radical (OH), nitrate radical (NO3), and ozone (O3). During the daytime, when light penetrates the plumes, BBVOCs are oxidized mainly by O3 and OH. In contrast, at night or in optically dense plumes, BBVOCs are oxidized mainly by O3 and NO3. This work focuses on the transition between daytime and nighttime oxidation, which has significant implications for the formation of secondary pollutants and loss of nitrogen oxides () and has been understudied. We present wildfire plume observations made during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality), a field campaign involving multiple aircraft, ground, satellite, and mobile platforms that took place in the United States in the summer of 2019 to study both wildfire and agricultural burning emissions and atmospheric chemistry. We use observations from two research aircraft, the NASA DC-8 and the NOAA Twin Otter, with a detailed chemical box model, including updated phenolic mechanisms, to analyze smoke sampled during midday, sunset, and nighttime. Aircraft observations suggest a range of NO3 production rates (0.1&ndash;1.5&thinsp;ppbv&thinsp;h&minus;1) in plumes transported during both midday and after dark. Modeled initial instantaneous reactivity toward BBVOCs for NO3, OH, and O3 is 80.1&thinsp;%, 87.7&thinsp;%, and 99.6&thinsp;%, respectively. Initial NO3 reactivity is 10&ndash;104 times greater than typical values in forested or urban environments, and reactions with BBVOCs account for &gt;97&thinsp;% of NO3 loss in sunlit plumes (jNO2 up to ), while conventional photochemical NO3 loss through reaction with NO and photolysis are minor pathways. Alkenes and furans are mostly oxidized by OH and O3 (11&thinsp;%&ndash;43&thinsp;%, 54&thinsp;%&ndash;88&thinsp;% for alkenes; 18&thinsp;%&ndash;55&thinsp;%, 39&thinsp;%&ndash;76&thinsp;%, for furans, respectively), but phenolic oxidation is split between NO3, O3, and OH (26&thinsp;%&ndash;52&thinsp;%, 22&thinsp;%&ndash;43&thinsp;%, 16&thinsp;%&ndash;33&thinsp;%, respectively). Nitrate radical oxidation accounts for 26&thinsp;%&ndash;52&thinsp;% of phenolic chemical loss in sunset plumes and in an optically thick plume. Nitrocatechol yields varied between 33&thinsp;% and 45&thinsp;%, and NO3 chemistry in BB plumes emitted late in the day is responsible for 72&thinsp;%&ndash;92&thinsp;% (84&thinsp;% in an optically thick midday plume) of nitrocatechol formation and controls nitrophenolic formation overall. As a result, overnight nitrophenolic formation pathways account for 56&thinsp;%&plusmn;2&thinsp;% of NOx loss by sunrise the following day. In all but one overnight plume we modeled, there was remaining NOx (13&thinsp;%&ndash;57&thinsp;%) and BBVOCs (8&thinsp;%&ndash;72&thinsp;%) at sunrise. &nbsp;</p

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Evaluation of the accuracy of thermal dissociation CRDS and LIF techniques for atmospheric measurement of reactive nitrogen species

Abstract. The sum of all reactive nitrogen species (NOy) includes NOx (NO2 + NO) and all of its oxidized forms, and the accurate detection of NOy is critical to understanding atmospheric nitrogen chemistry. Thermal dissociation (TD) inlets, which convert NOy to NO2 followed by NO2 detection, are frequently used in conjunction with techniques such as laser induced fluorescence (LIF) and cavity ringdown spectroscopy (CRDS) to measure total NOy when set at &gt; 600 °C, or speciated NOy when set at intermediate temperatures. We report the conversion efficiency of known amounts of several representative NOy species to NO2 in our TD-CRDS instrument, under a variety of experimental conditions. We find that the conversion efficiency of HNO3 is highly sensitive to the flow rate and the residence time through the TD inlet, as well as the presence of other species that may be present during ambient sampling, such as ozone (O3). Conversion of HNO3 at 400 °C, nominally the set point used to selectively convert organic nitrates, can range from 2–6 % and may represent an interference in measurement of organic nitrates under some conditions. The conversion efficiency is strongly dependent on the operating characteristics of individual quartz ovens, and should be well calibrated prior to use in field sampling. We demonstrate quantitative conversion of both gas phase N2O5 and particulate ammonium nitrate in the TD inlet at 650 °C, the temperature normally used for conversion of HNO3. N2O5 has two thermal dissociation steps, one at low temperature representing dissociation to NO2 and NO3, and one at high temperature representing dissociation of NO3, which produces exclusively NO2 and not NO. We also find a significant interference from partial conversion (5–10 %) of NH3 to NO at 650 °C in the presence of representative (50 ppbv) levels of O3 in dry zero air. Although this interference appears to be suppressed when sampling ambient air, we nevertheless recommend regular characterization of this interference using standard additions of NH3 to TD instruments that convert reactive nitrogen to NO or NO2. </jats:p

Prospective Validation of the Emergency Surgery Score in Emergency General Surgery

BACKGROUND The Emergency Surgery Score (ESS) was recently developed and retrospectively validated as an accurate mortality risk calculator for emergency general surgery. We sought to prospectively validate ESS, specifically in the high-risk nontrauma emergency laparotomy (EL) patient. METHODS This is an Eastern Association for the Surgery of Trauma multicenter prospective observational study. Between April 2018 and June 2019, 19 centers enrolled all adults (aged \u3e18 years) undergoing EL. Preoperative, intraoperative, and postoperative variables were prospectively and systematically collected. Emergency Surgery Score was calculated for each patient and validated using c-statistic methodology by correlating it with three postoperative outcomes: (1) 30-day mortality, (2) 30-day complications (e.g., respiratory/renal failure, infection), and (3) postoperative intensive care unit (ICU) admission. RESULTS A total of 1,649 patients were included. The mean age was 60.5 years, 50.3% were female, and 71.4% were white. The mean ESS was 6, and the most common indication for EL was hollow viscus perforation. The 30-day mortality and complication rates were 14.8% and 53.3%; 57.0% of patients required ICU admission. Emergency Surgery Score gradually and accurately predicted 30-day mortality; 3.5%, 50.0%, and 85.7% of patients with ESS of 3, 12, and 17 died after surgery, respectively, with a c-statistic of 0.84. Similarly, ESS gradually and accurately predicted complications; 21.0%, 57.1%, and 88.9% of patients with ESS of 1, 6, and 13 developed postoperative complications, with a c-statistic of 0.74. Emergency Surgery Score also accurately predicted which patients required intensive care unit admission (c-statistic, 0.80). CONCLUSION This is the first prospective multicenter study to validate ESS as an accurate predictor of outcome in the EL patient. Emergency Surgery Score can prove useful for (1) perioperative patient and family counseling, (2) triaging patients to the intensive care unit, and (3) benchmarking the quality of emergency general surgery care

Prospective Validation of the Emergency Surgery Score in Emergency General Surgery

BACKGROUND The Emergency Surgery Score (ESS) was recently developed and retrospectively validated as an accurate mortality risk calculator for emergency general surgery. We sought to prospectively validate ESS, specifically in the high-risk nontrauma emergency laparotomy (EL) patient. METHODS This is an Eastern Association for the Surgery of Trauma multicenter prospective observational study. Between April 2018 and June 2019, 19 centers enrolled all adults (aged \u3e18 years) undergoing EL. Preoperative, intraoperative, and postoperative variables were prospectively and systematically collected. Emergency Surgery Score was calculated for each patient and validated using c-statistic methodology by correlating it with three postoperative outcomes: (1) 30-day mortality, (2) 30-day complications (e.g., respiratory/renal failure, infection), and (3) postoperative intensive care unit (ICU) admission. RESULTS A total of 1,649 patients were included. The mean age was 60.5 years, 50.3% were female, and 71.4% were white. The mean ESS was 6, and the most common indication for EL was hollow viscus perforation. The 30-day mortality and complication rates were 14.8% and 53.3%; 57.0% of patients required ICU admission. Emergency Surgery Score gradually and accurately predicted 30-day mortality; 3.5%, 50.0%, and 85.7% of patients with ESS of 3, 12, and 17 died after surgery, respectively, with a c-statistic of 0.84. Similarly, ESS gradually and accurately predicted complications; 21.0%, 57.1%, and 88.9% of patients with ESS of 1, 6, and 13 developed postoperative complications, with a c-statistic of 0.74. Emergency Surgery Score also accurately predicted which patients required intensive care unit admission (c-statistic, 0.80). CONCLUSION This is the first prospective multicenter study to validate ESS as an accurate predictor of outcome in the EL patient. Emergency Surgery Score can prove useful for (1) perioperative patient and family counseling, (2) triaging patients to the intensive care unit, and (3) benchmarking the quality of emergency general surgery care